(CBS) Too much television may turn a 5-year-old into a real problem child by the time they turn 7, according to a new study.

British researchers looked at a representative sample of over 11,000 kids born between 2000 and 2002, and found those who watched television longer than three hours per day were more likely to develop antisocial behaviors such as fighting, stealing or bullying.

"It is a very, very small effect we found," study author Dr. Alison Parkes, a researcher at the MRC Social and Public Health Sciences Unit of the University of Glasgow, told WebMD. However, "It could be the tip of the iceberg and if we knew what they were watching, we might find more of an effect."

All children in the study were enrolled in a long-running pool or millennium babies meant to track the long term health and development of British children.

Mothers were given questionnaires when their kids were ages 5 and 7, which measured conduct problems, emotional symptoms, poor attention span/hyperactivity, difficulties making friends, and empathy and concern for others (which are considered "pro-social" behaviors).

They were also asked how often their child watched television or played computer and video games at age five.

Researchers found almost two-thirds of the children watched TV for one to three hours a day, with 15 percent reporting more than three hours of viewing time. Less than 2 percent of surveyed children watched no television at all. Only three percent of children played video games more than three hours per day.

After ruling out other factors like family characteristics, the researchers discovered that watching more than three hours of TV per day was associated with a small but statistically significant increase in risk for antisocial behavior and conduct problems. Increased television viewing, however, was not associated with emotional problems or attention issues, and time spent playing video games also had no impact on the results.

The study's authors concede the link between conduct problems and television time may be indirect, and a factor of the added inactivity, sleeping difficulties or impaired development associated with too much screen time.

The findings, which were published March 25 in the Archives of Disease in Childhood, showed an association and not cause and effect. The researchers said more work is needed to determine a causal link, but in the meantime, they suggest a cautionary approach to heavy television use in young children.

The American Academy of Pediatrics recommends that children and teen spend no more of two hours per day watching television, which should be "high-quality content."

Many children spend an average of seven hours per day, according to the academy.

Sonia Livingstone, professor of social psychology, at the London School of Economics, told the BBC the findings were a "good reason to ask why some children spend so much time watching television."

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